An inverted pendulum type mobile unit in this description includes a vehicle body and a rotator with a circular cross section (such as a wheel) which is coupled to the vehicle body in such a way that the vehicle body can tilt in the longitudinal direction of the mobile unit and is capable of moving by the rotation of the rotator while maintaining the state where the center of gravity of the vehicle body or the center of gravity of the total mass of the vehicle and a subject such as a user that is supported on the vehicle body is located above the rotation center of the rotator.
There have been proposals for a control method of an inverted pendulum type mobile unit. In an inverted pendulum type mobile unit of a related art, it is typical to detect a tilt angle of a vehicle body with respect to the vertical by a tilt angle sensor which is placed in the mobile unit and perform inverted pendulum stabilization control and traveling control using the detected tilt angle as an input variable. The inverted pendulum type mobile unit which employs such a control method is disclosed in the patent document 1.
The inverted pendulum type mobile unit which is disclosed in the patent document 1 includes wheels that are attached at the left and right sides of a vehicle body and two motors that respectively drive the left and right wheels independently. The inverted pendulum type mobile unit which is disclosed in the patent document 1 further includes a tilt angle sensor (specifically, an acceleration sensor) that detects a tilt angle of the vehicle body in the longitudinal direction of the mobile unit, a tilt angular rate sensor (specifically, a rate gyro) that detects a tilt angular rate, and a controlling portion that performs the inverted pendulum stabilization control for maintaining the inverted position of the vehicle body and the traveling control in the longitudinal direction using the tilt angle and the tilt angular rate which are detected by the tilt angle sensor and the tilt angular rate sensor as input variables.
In the inverted pendulum type mobile unit which is disclosed in the patent document 1, the forward and backward traveling of the mobile unit is controlled according to the tilt of the vehicle body by the shift in the center of gravity of a user. In the inverted pendulum type mobile unit which travels by a user's control of the tilt angle of the vehicle body, an acceleration of the mobile unit is determined as a result of performing the control loop for maintaining a dynamically balanced inverted state, and a velocity is determined as a result of the traveling of the mobile unit with the determined acceleration. Since the controlled variable which is designated by a user is the tilt angle of the vehicle body, the mobile unit is likely to behave in a way that is not intended by the user. Because the above-described handling of the inverted pendulum type mobile unit by the tilt angle of the vehicle body differs significantly from the handling of a passenger car, which controls the velocity of the mobile unit by the adjustment of accelerator opening made by a driver, the above-described way of controlling the mobile unit is generally difficult.
On the other hand, an inverted pendulum type mobile unit which performs the inverted pendulum stabilization control and the traveling control toward a velocity target value which is input by a user or the like, rather than the tilt angle of a vehicle body, as an input variable is also proposed (cf. e.g. the patent documents 2 and 3).
The patent document 2 discloses the inverted pendulum type mobile unit which has a joystick for inputting a fictitious signal that is deemed to be a tilt parameter that includes at least one of a tilt angle or a tilt angular rate of a vehicle body and controls the forward and backward traveling of the mobile unit according to the manipulation of the joystick by a user. The patent document 2 describes a tilt angle target value and a translational velocity target value of a vehicle body as specific parameters which are associated with a fictitious signal that is generated according to the degree of manipulation of the joystick.
In the inverted pendulum type mobile unit which is disclosed in the patent document 2, when the degree of manipulation of the joystick is associated with a velocity target value such as a translational velocity of the mobile unit or a rotation angular velocity of wheels, the mobile unit can travel forward and backward at the velocity target value which is input by the manipulation of the joystick by performing the combination of the traveling control which generates a torque command value to a motor so as to generate a translational velocity or a rotation angular velocity of wheels which is equal to the velocity target value according to the velocity target value which is given by the joystick manipulation and the inverted pendulum stabilization control which generates a torque command value so as to maintain the inverted position of the vehicle body using a tilt angle and a tilt angular rate of the vehicle body as input variables.
The inverted pendulum type mobile unit which is disclosed in the patent document 3 detects at least one of a tilt angle and a tilt angular rate of a vehicle body and performs the inverted pendulum stabilization control of the inverted pendulum type mobile unit using the detected one or both of tilt angle and tilt angular rate as an input value. Specifically, the inverted pendulum type mobile unit which is disclosed in the patent document 3 includes a gyro sensor that detects a tilt angular rate and performs the inverted pendulum stabilization control so as to bring the tilt angular rate that is detected by the gyro sensor to zero. Further, the inverted pendulum type mobile unit which is disclosed in the patent document 3 is capable of inputting a velocity target value of the mobile unit and it performs the traveling control so that the velocity of the mobile unit becomes the input velocity target value in addition to the above-described inverted pendulum stabilization control.    [Patent document 1] Japanese Unexamined Patent Application Publication No. 2005-94898    [Patent document 2] Japanese Unexamined Patent Application Publication No. 4-201793    [Patent document 3] Japanese Unexamined Patent Application Publication No. 2004-295430